Cisco IGX 8400 Series Switches

Document ID: 44960

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
Using the cnfcmb Command
Related Information

Introduction

This document describes the benefits of the cnfcmb command—you can increase the efficiency of these Cisco IGX ATM trunk cards:

• Asynchronous Transfer Mode (ATM) Line Module (ALM)

• Broadband Trunk Module (BTM)

• Universal Switching Module (UXM)

Prerequisites

Requirements

Readers of this document should be knowledgeable of:

• Cisco IGX ATM trunk cards

Components Used

The information in this document is based on these software versions:

• Cisco WAN Switching System Software version 8.5.x and later

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

For more information on document conventions, refer to the Cisco Technical Tips Conventions.

Using the cnfcmb Command

The cnfcmb command determines the length of time, after a FastPacket (FP) is put in a cell, that the IGX trunk waits for the second FP before it sends the cell half-filled (without the second FP). The combination of FPs is done on a per-virtual circuit (VC) basis—if a particular cell is to have two FPs in it, both FPs must be from the same permanent virtual circuit (PVC). You can configure this parameter for all traffic types.

If the FP-to-ATM cell combining values for connections are less than the minimum values specified in this table, trunk bandwidth may be wasted. In the least efficient scenario, only one FP (24 bytes) is transmitted as the payload of one ATM cell (53 bytes).

This table lists recommended values for all voice traffic types:

In most cases, you can use the cnfcmb command to significantly increase available trunk bandwidth. However, if you configure the value too high, you may introduce an extra delay on your network.

The cnfcmb command is a SERVICE level command and is known as a system wide command—you need to set it only on one node.

Related Information

• Cisco WAN Switching Solutions - Cisco Documentation
• Guide to New Names and Colors for WAN Switching Products
• Downloads - WAN Switching Software
• Technical Support - Cisco Systems